The present invention relates to an improved electromagnetic spring-wound clutch which may be advantageously employed to connect an air conditioning compressor to an engine of an automotive vehicle.
An electromagnetic spring-wound clutch of the general type to which the present invention relates is disclosed in U.S. Pat. No. 3,735,847 and comprises coaxial input and output members. A clutch disc is rotatably provided on the input member. Furthermore, a coil-wound spring is wound around the input member and connected at its opposite ends to the clutch disc and output member. An electromagnetic coil attracts the clutch disc into frictional engagement with the input member, causing the coil-wound spring to be tightly wound the input member and drivably connect the input member to the output member. When the coil is de-energized, the clutch disc disengages from the input member, and the coil-wound spring releases the input member for rotation relative to the output member.
A major problem in this type of clutch is obtaining fast and smooth disengagement of the clutch plate. More specifically, the clutch plate tends to vibrate during disengagement, causing noise, and furthermore does not disengage completely parallel to the input member. In extreme cases, the clutch plate may be deformed or even break. A prior art attempt to overcome this problem involves an arrangement in which the coil-wound spring is stretched axially by the clutch plate when the coil is energized, and disengages the clutch plate when the coil is de-energized due to its resilience. However, due to the large spring constant required to drivably connect the input member to the output member, the coil must have an excessive magnetomotive force to stretch the coil-wound spring. Such a large coil cannot be fit into the clutch in a practical manner.